I THALES TO LUCRETIUS 23 



of things by particles of matter ruled in their move- 

 ments by unvarying laws. This theory he works all 

 round, explaining the processes by which the atoms 

 unite to carry on the birth, growth, and decay of 

 things, the variety of which is due to variety of form 

 of the atoms and to differences in modes of their 

 combination ; the combinations being determined by 

 the affinities or properties of the atoms themselves, 

 'since it is absolutely decreed, what each thing can 

 and what it cannot do, by the conditions of nature.' 

 Change is the law of the universe ; what is, will 

 perish, but only to reappear in another form. 

 Death is * the only immortal ' ; and it is that and 

 what may follow it, which are the chief tormentors 

 of men. ' This terror of the soul, therefore, and this 

 darkness, must be dispelled, not by the rays of the 

 sun or the bright shafts of day, but by the outward 

 aspect and harmonious plan of nature/ Lucretius 

 explains that the soul, which he places in the centre of 

 the breast, is also formed of very minute atoms of heat, 

 wind, calm air, and a finer essence, the proportions 

 of which determine the character of both men and 

 animals. It dies with the body, in support of which 

 statement Lucretius advances seventeen arguments, 

 so determined is he to ' deliver those who through 

 fear of death are all their lifetime subject to bondage.' 

 These themes fill the first three books. In the 

 fourth he grapples with the mental problems of 

 sensation and conception, and explains the origin of 

 belief in immortality as due to ghosts and appari- 

 tions which appear in dreams. 'When sleep has 

 prostrated the body, for no other reason does the 

 mind's intelligence wake, except because the very 



